Semiconductor structure integrated with magnetic tunneling junction

ABSTRACT

The present disclosure provides a semiconductor structure. The semiconductor structure includes a substrate, a transistor region, a metal interconnect, and a magnetic tunneling junction (MTJ). The transistor region includes a gate over the substrate, and a doped region is at least partially in the substrate. The metal interconnect is over the doped region. The metal interconnect includes a metal via. The MTJ is entirely underneath the metal interconnect and between the doped region and the metal via, and a diameter of a bottom surface of the MTJ is greater than a diameter of an upper surface of the MTJ.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application to prior-filed U.S.application Ser. No. 16/717,747, filed 17 Dec. 2019, and further claimsthe benefit of prior-filed application Ser. No. 14/871,685, filed Sep.30, 2015 and granted as U.S. Pat. No. 10,068,945, and prior-filedapplication Ser. No. 16/120,990, filed Sep. 4, 2018 and granted as U.S.Pat. No. 10,510,804, under 35 U.S.C. 120.

FIELD

The present disclosure relates to a semiconductor structure integratedwith a magnetic tunneling junction and method of manufacturing thesemiconductor structure integrated with the magnetic tunneling junction.

BACKGROUND

With increasing use of portable computing devices and wirelesscommunication devices, memory devices may require higher density, lowerpower, and/or nonvolatile properties. Magnetic memory devices may beable to satisfy the aforementioned technical requirements.

An example data storing mechanism for a magnetic memory device is atunnel magneto resistance (TMR) effect of a magnetic tunnel junction(MTJ). For example, a magnetic memory device with a MTJ have beendeveloped such that an MTJ may have a TMR ratio of several hundred toseveral thousand percent.

A magnetoresistive random access memory (MRAM) cell is formed by amagnetic tunneling junction (MTJ), which is a structure in which twoferromagnetic layers are separated by a thin insulating barrier. When apotential difference is applied across the two ferromagnetic layers,current flows through the insulating barrier by quantum mechanicaltunneling. The resistance of the MTJ depends on the relative orientationof magnetic elements in the two ferromagnetic layers. The resistance islowest when the magnetizations are aligned in parallel and highest whenthey are anti-parallel. One of the relative orientations can be used torepresent a “1” and the other to represent a “0”. In general, themagnetic orientation of one of the layers (the pinned layer) is keptfixed while the magnetic orientation of the other layer (the free layer)is set in a write operation. The state of the MRAM cell can be queriedby measuring the junction's resistance. For an array of MRAM cells toprovide reliable data storage, a sufficiently great difference inresistance between the two possible states must be realized for eachcell in the array.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a diagram illustrating a read window of a semiconductorstructure integrated with an MTJ, according to some embodiments of thepresent disclosure;

FIG. 2 is a cross section of a semiconductor structure integrated withan MTJ, according to some embodiments of the present disclosure;

FIG. 3 is a cross section of a semiconductor structure integrated withan MTJ, according to some embodiments of the present disclosure;

FIG. 4 is a top view of one layer of a semiconductor structureintegrated with an MTJ, according to some embodiments of the presentdisclosure;

FIG. 5 is a diagram illustrating layers constituting an MTJ, accordingto some embodiments of the present disclosure;

FIG. 6 is a diagram illustrating layers constituting an MTJ, accordingto some embodiments of the present disclosure;

FIG. 7 is a cross section of a semiconductor structure integrated withan MTJ in a first region and a second region, according to someembodiments of the present disclosure;

FIG. 8 is a cross section of a semiconductor structure integrated withan MTJ in a first region, according to some embodiments of the presentdisclosure;

FIG. 9 is a cross section of a semiconductor structure integrated withan MTJ in a first region and a second region, according to someembodiments of the present disclosure;

FIG. 10 is a top view of one layer of a semiconductor structureintegrated with an MTJ, according to some embodiments of the presentdisclosure;

FIG. 11 to FIG. 26 show fragmental cross-sectional views of theformation of a semiconductor structure integrated with an MTJ in a firstregion and a second region, according to some embodiments of the presentdisclosure.

DETAILED DESCRIPTION OF THE INVENTION

This description of illustrative embodiments is intended to be read inconnection with the accompanying drawings, which are to be consideredpart of the entire written description. In the description ofembodiments disclosed herein, any reference to direction or orientationis merely intended for convenience of description and is not intended inany way to limit the scope of the present invention. Relative terms suchas “lower,” “upper,” “horizontal,” “vertical,”, “above,” “below,” “up,”“down,” “top” and “bottom” as well as derivative thereof (e.g.,“horizontally,” “downwardly,” “upwardly,” etc.) should be construed torefer to the orientation as then described or as shown in the drawingunder discussion. These relative terms are for convenience ofdescription only and do not require that the apparatus be constructed oroperated in a particular orientation. Terms such as “attached,”“affixed,” “connected” and “interconnected,” refer to a relationshipwherein structures are secured or attached to one another eitherdirectly or indirectly through intervening structures, as well as bothmovable or rigid attachments or relationships, unless expresslydescribed otherwise. Moreover, the features and benefits of theinvention are illustrated by reference to the preferred embodiments.Accordingly, the invention expressly should not be limited to suchpreferred embodiments illustrating some possible non-limitingcombination of features that may exist alone or in other combinations offeatures; the scope of the invention being defined by the claimsappended hereto.

In the drawings, like reference numbers are used to designate like orsimilar elements throughout the various views and illustrativeembodiments of the present invention are shown and described. Thefigures are not necessarily drawn to scale, and in some instances thedrawings have been exaggerated and/or simplified in places forillustrative purposes only. One of ordinary skill in the art willappreciate the many possible applications and variations of the presentinvention based on the following illustrative embodiments of the presentinvention.

Enlarging a read window in an MRAM cell can be achieved by obtaining anarrower full-width-half-maxima (FWHM) of the device count peak withrespect to the resistance level. Referring to FIG. 1 , FIG. 1 is adiagram illustrating a read window of a semiconductor structureintegrated with an MTJ, according to some embodiments of the presentdisclosure. An upper diagram and lower diagram of FIG. 1 show an X axisof resistance and a Y axis of counts of number of devices tested. Theupper diagram of FIG. 1 illustrates an ideal case where only devicesignal is accounted and rendering a narrow FWHM on both the Gaussianpeak 1 and Gaussian peak 2. In some embodiments, the Gaussian peak 1refers to a “low” logic level (R_(low)) while the Gaussian peak 2 refersto a “high” logic level (R_(high)).

Similarly, the lower diagram of FIG. 1 illustrates a real case where notonly device 1 o signal but also a summation of signal from routing metalare accounted and rendering a broadened FWHM on both the Gaussian peak1′ and Gaussian peak 2′. In some embodiments, the Gaussian peak 1′refers to a “low” logic level (R_(low)) while the Gaussian peak 2′refers to a “high” logic level (R_(high)).

A read window referred herein is a range of a specific resistancearbitrarily chosen between the “low” logic level (Rim) and the “high”logic level (R_(high)). Comparing the read window of the upper diagramand the lower diagram of FIG. 1 , the read window Wr1 of the upperdiagram is substantially wider than the read window Wr2 of the lowerdiagram. In some embodiments, the lower diagram of FIG. 1 is derivedfrom a real semiconductor device where an MRAM cell is positionedbetween two sequential metal layers M_(x) and M_(x+1). In someembodiments, the MRAM cell is formed after the fourth metal layer M₄ andbefore the fifth metal layer M₅. The metal layer referred herein can bedirected to horizontal metallic connection within dielectric materials,as opposed to vertical metallic connection, or so-called “via”. In suchcondition, the signal of the MRAM cell inevitably include all theinformation from previous metal interconnects M₁, M₂, M₃, includingmetal lines at different levels and all the vias connecting theaforesaid metal lines.

The information contributed from the aforesaid previous metal layers,the MRAM cell, and the underlying transistor can be different fromdevice to device. For example, process variation may cause thethicknesses or the lengths of different metal layer or vias to form afinite distribution. In other words, undergoing identical manufacturingoperations, device A and device B may demonstrate different “low” logiclevel (R_(low)) and the different “high” logic level (R_(high)). Whentaking all the devices fabricated into account, FWHM of the “low” logiclevel (R_(low)) and the “high” logic level (R_(high)) are broadened asshown in the lower diagram of FIG. 1 , deviated from narrow counterpartof the ideal case shown in the upper diagram of FIG. 1 .

Pursuing a narrower read window of a memory device is one intendedpurpose of the present disclosure.

The process variation can be magnified if the manufacturing variation atlower metal layer is further carried to the upper metal layer. Forexample, chemical mechanical polishing (CMP) is an operation forDamascene metal structure. When a CMP operation in the lower metal layerdoes not provide a planarized surface, the small height variation ismagnified when reaching the upper metal layer, causing a more seriousheight variation. It is understood that structural variation of metallayers can directly influence series resistance of the metal layers.When all the devices fabricated are taken into account, seriesresistance of the metal layers can also form a distribution, broadeningthe FWHM of the peaks of the “low” logic level (R_(low)) and that of the“high” logic level (R_(high)).

To narrow the FWHM of the R_(low) and R_(high) peaks, the presentdisclosure provides a memory cell formed before all the metal layerabove a transistor region. For example, an MRAM cell can be formedbefore the first metal interconnect M₁. Alternatively stated, the MRAMcell described herein is formed during the middle-end-of-line (MEOL)operation and before the back-end-of-line (BEOL) operation. In someembodiments, the MEOL operation refers to all the operation after theformation of the gate and source/drain of a transistor and before theformation of any metal layers, or Cu-process. Particular MEOL operationincludes the formation of conductive plug structure from the gate orsource/drain region, and the formation of dielectric layer encapsulatingthe transistor structure. Particular BEOL operation includes all theoperations after the formation of the metal layer, or the Cu-process.

Forming an MRAM cell before metal layers minimizes the signal from metalroutings and thus a narrower FWHM of the R_(low) and R_(high) peaks canbe obtained. Furthermore, the subsequent processing window for CMPoperations in the BEOL can be widened due to the fact that thecontribution of process variation in BEOL generates a smaller impact tothe read window as far as a memory device is concerned.

Referring to FIG. 2 , FIG. 2 is a cross section of a semiconductorstructure 10 integrated with an MTJ, according to some embodiments ofthe present disclosure. In FIG. 2 , transistor region 11, which aresymbolized using a transistor, may be formed at a surface of substrate100. In alternative embodiments, substrate 100 is a dielectricsubstrate, and no active devices are formed on the dielectric substrate,although passive devices such as capacitors, inductors, resistors, andthe like may be formed. Contact plugs 113 are formed in inter-layerdielectric (ILD) 115, and may be electrically coupled to transistorregion 11. The semiconductor device 11 and the contact plugs 113 can becollectively referred to as a transistor region. The semiconductordevice 11 includes a gate 103 and doped regions 105 a, 105 b at leastpartially in the substrate 100. FIG. 2 shows a planar transistor havinga doped region in the substrate 100. However, the present disclosure isnot limited thereto. Any non-planar transistor, such as a FinFETstructure, can have raised doped regions 105 a, 105 b.

Interconnect structure 12, which includes metal lines 117 and vias 119therein and electrically coupling to transistor region 11, is formedover ILD 115. Metal lines 117 and vias 119 may be formed ofsubstantially pure copper (for example, with a weight percentage ofcopper being greater than about 90 percent, or greater than about 95percent) or copper alloys, and may be formed using the single and/ordual damascene processes. Metal lines 117 and vias 119 may be, or maynot be, substantially free from aluminum. Interconnect structure 12includes a plurality of metal interconnects, namely M₁, M₂ . . . M_(top)111, wherein metal interconnect M₁ is the metal lines and vias closestto the ILD 115, while metal interconnect M_(top) 111 is the top metallines and vias that are farthest to the ILD 115. Throughout thedescription, the term “metal interconnects” refers to the collection ofthe metal lines and vias in the same layer. Metal interconnects M₁through M_(top) 111 are formed in inter-metal dielectrics (IMDs) 115′,which may be formed of oxides such as un-doped Silicate Glass (USG),Fluorinated Silicate Glass (FSG), low-k dielectric materials, or thelike. The low-k dielectric materials may have k values lower than 3.8,although the dielectric materials of IMDs 115′ may also be close to 3.8.In some embodiments, the k values of the low-k dielectric materials arelower than about 3.0, and may be lower than about 2.5.

In FIG. 2 , the semiconductor substrate 100 may be but is not limitedto, for example, a silicon substrate. In an embodiment, substrate 100 isa semiconductor substrate, such as a silicon substrate, although it mayinclude other semiconductor materials, such as silicon germanium,silicon carbide, gallium arsenide, or the like. In the presentembodiment, the substrate 100 is a p-type semiconductor substrate(P-Substrate) or an n-type semiconductor substrate (N-Substrate)comprising silicon. Alternatively, the substrate 100 includes anotherelementary semiconductor, such as germanium; a compound semiconductorincluding silicon carbide, gallium arsenic, gallium phosphide, indiumphosphide, indium arsenide, and/or indium antimonide; an alloysemiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP,and/or GaInAsP; or combinations thereof. In yet another alternative, thesubstrate 100 is a semiconductor on insulator (SOI). In otheralternatives, semiconductor substrate 100 may include a doped epi layer,a gradient semiconductor layer, and/or a semiconductor layer overlyinganother semiconductor layer of a different type, such as a silicon layeron a silicon germanium layer. The substrate 100 may or may not includedoped regions, such as a p-well, an n-well, or combination thereof.

A number of shallow trench isolation (STI) regions 101 are formed in thesemiconductor substrate 100. The STI regions 101, which may be formed ofsuitable dielectric materials, may be provided to isolate a transistorelectrically from neighboring semiconductor devices such as othertransistors. The STI regions 101 may, for example, include an oxide(e.g., Ge oxide), an oxynitride (e.g., GaP oxynitride), silicon dioxide(SiO₂), a nitrogen-bearing oxide (e.g., nitrogen-bearing SiO₂), anitrogen-doped oxide (e.g., N₂-implanted SiO₂), silicon oxynitride(Si_(x)O_(y)N_(z)), and the like. The STI regions may also be formed ofany suitable “high dielectric constant” or “high K” material, where K isgreater than or equal to about 8, such as titanium oxide (Ti_(x)O_(y),e.g., TiO₂), tantalum oxide (Ta_(x)O_(y), e.g., Ta₂O₅), barium strontiumtitanate (BST, BaTiO₃/SrTiO₃), and the like. Alternatively, the STIregions may also be formed of any suitable “low dielectric constant” or“low K” dielectric material, where K is less than or equal to about 4.

Still in FIG. 2 , the ILD 115 or IMD 115′ may be formed by a variety oftechniques for forming such layers, e.g., chemical vapor deposition(CVD), low-pressure CVD (LPCVD), plasma-enhanced CVD (PECVD), sputteringand physical vapor deposition (PVD), thermal growing, and the like. Thedielectric layer above the semiconductor substrate 100 may have athickness ranging up to approximately 50 Angstrom, for example, and maybe formed from a variety of dielectric materials and may, for example,be an oxide (e.g., Ge oxide), an oxynitride (e.g., GaP oxynitride),silicon dioxide (SiO₂), a nitrogen-bearing oxide (e.g., nitrogen-bearingSiO₂), a nitrogen-doped oxide (e.g., N₂-implanted SiO₂), siliconoxynitride (Si_(x)O_(y)N_(z)), and the like.

Still referring to FIG. 2 , metal interconnects M₁, M₂, and M_(top)include conductive material in IMDs 115′. The conductive material can byTa, Cu, Al, or and other suitable metal. The IMD 115′ can include one ormore layers of any suitable dielectric(s). The dielectric can be SiO₂.In some embodiments, the dielectric is a low-k dielectric. A low-kdielectric is a material having a dielectric constant lower than that ofsilicon dioxide. Examples of low-k dielectrics include organosilicateglasses (OSG) such as carbon-doped silicon dioxide, fluorine-dopedsilicon dioxide (otherwise referred to as fluorinated silica glass (orFSG), and organic polymer low-k dielectrics. Examples of organic polymerlow-k dielectrics include polyarylene ether, polyimide (PI),benzocyclobutene, and amorphous polytetrafluoroethylene (PTFE). A low-kdielectric can be applied by any suitable means, including for example,spin coating or CVD.

A memory structure, for example, an MRAM cell, is positioned between thesemiconductor device 11 and the interconnect structure 12. In someembodiments, an MTJ layer 201 consisting of multiple ferromagnetic andnon-ferromagnetic layers, having a lower electrode 202 and an upperelectrode 203 parallel with the multiple layers. For example, the lowerelectrode 202 can be made in contact with the contact plug 113 extendingfrom the semiconductor device 11. The upper electrode 203 can be made incontact with a via 119 of the first metal interconnect M₁. Note thefirst metal interconnect M₁ includes via 119 and metal lines 117 closestto the ILD 115. The upper electrode 203 is under the first metalinterconnect M₁, specifically, the upper electrode 203 is under a via119 of the first metal interconnect M₁. Furthermore, a protection layer204 covering at least a sidewall of the MTJ layer 201 is positioned overdielectric layers 206 a, 206 b. The protection layer 204 is configuredto prevent the sidewall of the MTJ layer 201 from oxidation or fromother contamination in the subsequent processing. The structuralintegrity of the MTJ layer 201 is crucial to the performance of thememory. In some embodiments, the dielectric layers 206 a, 206 b can bean oxide (e.g., Ge oxide), an oxynitride (e.g., GaP oxynitride), silicondioxide (SiO₂), a nitrogen-bearing oxide (e.g., nitrogen-bearing SiO₂),a nitrogen-doped oxide (e.g., N₂-implanted SiO₂), silicon oxynitride(Si_(x)O_(y)N_(z)), and the like. Moreover, another dielectric layer 205can be formed over the protection layer 204 and being level with theupper electrode 203 of the MRAM cell.

Referring to both FIG. 2 and FIG. 3 , FIG. 3 is a cross section of asemiconductor structure integrated with an MTJ, according to someembodiments of the present disclosure. In FIG. 2 , the lower electrode202 of the MRAM cell is electrically coupled with the doped region 105b. In some embodiments, the doped region 105 b is a drain or a source.In FIG. 3 , the lower electrode 202 of the MRAM cell is electricallycoupled with the gate 103. In some embodiments, the gate 103 of thesemiconductor device 11 can be a polysilicon gate or a metal gate. Asshown in FIG. 3 , a height T of the MTJ layer 201 is in a range of fromabout 150 Å to about 250 Å. Such height T is suitable for integrating anMTJ layer 201 into the MEOL operation, between the interconnectstructure 12 and the transistor region.

In FIG. 2 and FIG. 3 , the MRAM cell is disposed in the semiconductorstructure 10 in such a way that the first metal interconnect M₁, thegate 103, the doped regions 105 a, 105 b, and the MTJ layer 201 form aconductive loop. In other words, no matter the MRAM cell is positionedabove the doped regions 105 a, 105 b, or above the gate 103, the “low”logic level (R_(low)) and the “high” logic level (R_(high)) can bedetermined when a current travelling the aforesaid conductive loop. Inthis connection, conductive signal may no longer contain informationfrom upper metal layers M_(x) (x>1) and narrow down the read window ofthe MRAM cell.

Referring to FIG. 4 , FIG. 4 is a top view of one layer of asemiconductor structure integrated with an MTJ, according to someembodiments of the present disclosure. In some embodiments, FIG. 4 is atop view dissecting along line AA of FIG. 2 . From a top viewperspective, vias 119 of the first metal interconnect M₁ have a footprint of, for example, two circles 40. However, the foot print of thevias 119 of the first metal interconnect M₁ may not be limited thereto.Other geometrical shapes are within the contemplated scope of thepresent disclosure. On the surface of the dielectric layer 206 b, theMTJ layer 201 has a foot print of, for example, a circle 41. A bottom ofthe MTJ layer 201 may possess a diameter D1, and a top of the MTJ layer201 may possess a diameter D2 shown in dotted lines. In someembodiments, the diameter D1 of the MTJ layer 201 is in a range of fromabout 10 nm to about 60 nm. In some embodiments, the diameter D2 of theMTJ layer 201 is smaller than the diameter D1 by 20% to 50%.

FIG. 5 is a diagram illustrating multiple ferromagnetic andnon-ferromagnetic layers constituting an MTJ layer 201, according tosome embodiments of the present disclosure. Referring to FIG. 5 , theMTJ layer 201 may include ferromagnetic layers 15 al, 15 a 3 and 15 a 5,spacers 15 a 2 and 15 a 4, and a capping layer 15 a 6. The spacer 15 a 2is formed on the ferromagnetic layer 15 al. The ferromagnetic layer 15al is formed on the spacer 15 a 2. The spacer 15 a 2 is formed on theferromagnetic layer 15 a 3. The ferromagnetic layer 15 a 3 is formed onthe spacer 15 a 4. The capping layer 15 a 6 is formed on theferromagnetic layer 15 al. Each of the ferromagnetic layers 15 a 1, 15 a3 and 15 a 5 may include ferromagnetic material, which may be metal ormetal alloy, for example, Fe, Co, Ni, CoFeB, FeB, CoFe, FePt, FePd,CoPt, CoPd, CoNi, TbFeCo, CrNi or the like. The spacer 15 a 2 mayinclude non-ferromagnetic metal, for example, Ag, Au, Cu, Ta, W, Mn, Pt,Pd, V, Cr, Nb, Mo, Tc, Ru or the like. The spacer 15 a 4 may includeinsulator, for example, Al₂O₃, MgO, TaO, RuO or the like. The cappinglayer 15 a 6 may include non-ferromagnetic material, which may be ametal or an insulator, for example, Ag, Au, Cu, Ta, W, Mn, Pt, Pd, V,Cr, Nb, Mo, Tc, Ru, Ir, Re, Os, Al₂O₃, MgO, TaO, RuO or the like. Thecapping layer 15 a 6 may reduce write current of its associated magneticrandom-access memory (MRAM) cell. In some embodiments, spacer 15 a 4 andcapping layer 15 a 6 can be any suitable dielectrics materials.Dielectric materials that can be suitable for these layers include, forexample, SiN, SiO_(X), and SiON. In some embodiments, spacer 15 a 4 isformed from one or more materials selected from the group consisting ofSiN, SiO_(X), and SiON.

The ferromagnetic layer 15 al may function as a free layer 215 whosemagnetic polarity or magnetic orientation can be changed during writeoperation of its associated MRAM cell. The ferromagnetic layers 15 a 3,15 a 5 and the spacer 15 a 4 may function as a fixed or pinned layer 213whose magnetic orientation may not be changed during operation of itsassociated MRAM cell. It is contemplated that the MTJ layer 201 mayinclude an antiferromagnetic layer (not shown in FIG. 5 ) in accordancewith other embodiments. In some embodiments, the pinned layer 213 iscloser to the lower electrode 202 and thus the doped region 105 b thanthe free layer 215. Free layer 215 and pinned layer 213 can be anysuitable ferromagnetic or other material that performs similarly to aferromagnetic material. Materials that can be suitable include NiFe,CoFe, CoFeB. In some embodiments, free layer 215 includes CoFeB. In someembodiments, the pinned layer 213 includes either CoFe or COFeB.

In FIG. 5 , an upper surface of the MTJ layer 201 possesses a diameterD2, whereas a bottom surface of the MTJ layer 201 possesses a diameterD1. With reference to FIG. 4 , the 1 o diameter D1 is greater than thediameter D2. The ferromagnetic layer 15 a 5 is in contact with the lowerelectrode 202, and the capping layer 15 a 6 is in contact with the upperelectrode 203.

FIG. 6 is a diagram illustrating layers constituting an MTJ, accordingto some embodiments of the present disclosure. FIG. 6 is a diagramillustrating multiple ferromagnetic and non-ferromagnetic layersconstituting an MTJ layer 201′, according to some embodiments of thepresent disclosure. Referring to FIG. 6 , the MTJ layer 201′ may includeferromagnetic layers 15 al, 15 a 3 and 15 a 5, spacers 15 a 2 and 15 a4, and a capping layer 15 a 6. The spacer 15 a 2 is formed on theferromagnetic layer 15 al. The ferromagnetic layer 15 a 3 is formed onthe spacer 15 a 4. The spacer 15 a 4 is formed on the ferromagneticlayer 15 a 5. The ferromagnetic layer 15 a 5 is formed on the spacer 15a 2. The ferromagnetic layer 15 al is formed on the capping layer 15 a6. The ferromagnetic layer 15 al may function as a free layer 215 whosemagnetic polarity or magnetic orientation can be changed during writeoperation of its associated MRAM cell. The ferromagnetic layers 15 a 3,15 a 5 and the spacer 15 a 4 may function as a fixed or pinned layer 213whose magnetic orientation may not be changed during operation of itsassociated MRAM cell. It is contemplated that the MTJ layer 201 mayinclude an antiferromagnetic layer (not shown in FIG. 5 ) in accordancewith other embodiments.

In FIG. 6 , an upper surface of the MTJ layer 201 possesses a diameterD2, whereas a bottom surface of the MTJ layer 201 possesses a diameterD1. With reference to FIG. 4 , the diameter D1 is greater than thediameter D2. The capping layer 15 a 6 is in contact with the lowerelectrode 202, and the ferromagnetic layer 15 a 3 is in contact with theupper electrode 203. FIG. 6 is a reversed MTJ layers to that of FIG. 5 .In FIG. 5 , the electric current enters the ferromagnetic layer 15 a 5and exits the MTJ layer 201 through the capping layer 15 a 6. In FIG. 6, the electric current enters the ferromagnetic layer 15 a 3 and exitsthe MTJ layer 201′ through the capping layer 15 a 6. Depending fromdifferent current input directions, the stacking order of the MTJ layer201, 201′ can be changed accordingly. In some embodiments, the freelayer 215 is closer to the lower electrode 202 and thus the doped region105 b than the pinned layer 213.

Since manufacturing an MTJ layer 201 during MEOL operation increases thechance of exposing the MTJ layer 201 under high temperature environment,especially during the subsequent metallization operations in BEOL, theMTJ layer 201 introduced herein can endure the high temperatureenvironment without serious diffusion deteriorating memory deviceperformance.

FIG. 7 is a cross section of a semiconductor structure 20 integratedwith an MTJ in a first region 700 a and/or a second region 700 b,according to some embodiments of the present disclosure. Numeral labelsin FIG. 7 identical to those in FIG. 2 and FIG. 3 are referred to sameelements or equivalents thereof and are not repeated here forsimplicity. A first MTJ layer 201 a and a second MTJ layer 201 b arepositioned in the first region 700 a and the second region 700 b,respectively. The first region 700 a and the second region 700 b are twoportions of an integrated circuit each having at least one transistorstructure and the first region 700 a is not overlapping with the secondregion 700 b. However, the first region 700 a or the second region 700 beach does not have to possess an MTJ simultaneously. For example, asshown in FIG. 8 , a second region 700 b is free of an MTJ or any othermemory structure. Referring to FIG. 7 and FIG. 9 , the MTJs 201 a, 201 bin FIG. 7 are both electrically coupled to a doped region 105 b, whereasthe first MTJ 201 a of the first region 700 a in FIG. 9 is coupled to adoped region 105 b and the second MTJ 201 b of the second region 700 bis coupled to a gate 103.

As shown in FIG. 9 , a height T1 of the first MTJ layer 202 a in thefirst region 700 a is greater than a height T2 of the second MTJ layer202 b in the second region 700 b. In some embodiments, the bottomdiameter D1 of the first MTJ layer 202 a and the bottom diameter D1′ ofthe second MTJ layer 202 a are substantially the same, only heights ofthe two MTJ layers 202 a, 202 b are different. It is known that theamount of current sufficient to change the magnetic polarity of an MTJis related to the total volume of the MTJ. Since the diameters D1, D1′of the first MTJ layer 202 a and the second MTJ layer 202 b,respectively, are substantially identical, the second MTJ layer 202 bwith smaller height T2 is prone to change the magnetic polarity under asame current. In some embodiments, the MTJ layer 202 b can be an SRAMand the MTJ layer 202 a can be a flash.

Referring back to FIG. 7 , a diameter of the first MTJ 201 a isdifferent from that of the second MTJ 201 b. As shown in FIG. 10 , FIG.10 is a top view dissecting from line BB′ of a semiconductor structure20 integrated with an MTJ in the first region 700 a and the secondregion 700 b, according to some embodiments of the present disclosure.

In FIG. 10 , from a top view perspective, vias 119 of the first metalinterconnect M₁ in the first region 700 a have a foot print of, forexample, two circles 50 a. However, the foot print of the vias 119 ofthe first metal interconnect M₁ in the first region 700 a may not belimited thereto. Other geometrical shapes are within the contemplatedscope of the present disclosure. On the surface of the dielectric layer206 b, the MTJ layer 201 a in the first region 700 a has a foot printof, for example, a circle 51 a. A bottom of the MTJ layer 201 a maypossess a diameter D1, and a top of the MTJ layer 201 a may possess adiameter D2 shown in 1 o dotted lines. In some embodiments, the diameterD1 of the MTJ layer 201 a is in a range of from about 10 nm to about 60nm. In some embodiments, the diameter D2 of the MTJ layer 201 a issmaller than the diameter D1 by 20% to 50%.

In FIG. 10 , from a top view perspective, vias 119 of the first metalinterconnect M₁ in the second region 700 b have a foot print of, forexample, two circles 50 b. However, the foot print of the vias 119 ofthe first metal interconnect M₁ in the second region 700 b may not belimited thereto. Other geometrical shapes are within the contemplatedscope of the present disclosure. On the surface of the dielectric layer206 b, the MTJ layer 201 b in the second region 700 b has a foot printof, for example, a circle 51 b. A bottom of the MTJ layer 201 b maypossess a diameter D1′, and a top of the MTJ layer 201 b may possess adiameter D2′ shown in dotted lines. Note the diameter D1′ is smallerthan the diameter D1, and similarly, the diameter D2′ is smaller thanthe diameter D2. In some embodiments, memory in the first region 700 ais a Flash, and the memory in the second region 700 b is an SRAM.

In some embodiments, the diameter D1′ of the MTJ layer 201 b is in arange of from about 10 nm to about 60 nm. Note the diameter D1′ issmaller than the diameter D1, and similarly, the diameter D2′ is smallerthan the diameter D2. In some embodiments, the diameter D2′ of the MTJlayer 201 a is smaller than the diameter D1′ by 20% to 50%.

FIG. 11 to FIG. 26 show fragmental cross-sectional views of theformation of a semiconductor structure integrated with an MTJ in a firstregion 700 a and a second region 700 b, according to some embodiments ofthe present disclosure. In FIG. 11 , two transistor regions in a form oftransistors are formed over the substrate 100. As shown in FIG. 11 ,each transistor includes a gate 103 and doped regions 105 a, 105 b. Thetransistor in the first region 700 a and the second region 700 b areisolated by an STI 101. In some embodiments, the doped regions 105 a,105 b are raised source and drain, and the gate 103 is a metal gate.

In FIG. 12 , conductive plugs 113 are formed extending from the dopedregions 105 a, 105 b and the gate 103. A patterned ILD 115 is formedbefore the filling of the contact plugs 113. For example, through holesformed in the ILD 115 and subsequently being filled with electricallyconductive material, e.g., copper, gold or another suitable metal oralloy, to form a number of conductive plugs 113. The conductive plugs113 may be electrically connected to semiconductor devices such astransistors in the semiconductor substrate 100. The conductive plugs 113may be formed by a variety of techniques, e.g., electroplating,electroless plating, high-density ionized metal plasma (IMP) deposition,high-density inductively coupled plasma (ICP) deposition, sputtering,physical vapor deposition (PVD), chemical vapor deposition (CVD),low-pressure chemical vapor deposition (LPCVD), plasma-enhanced chemicalvapor deposition (PECVD), and the like. In FIG. 12 , a planarizationoperation is performed to expose a top surface of the conductive plugs113 and the top surface of the ILD 115.

In FIG. 13 , a stack of dielectric layers 206 a, 206 b, 206 c are formedover the planarized surface described in FIG. 12 . In some embodiments,the dielectric layers 206 a, 206 c can be of identical materials,whereas the dielectric layer 206 b can be another material having adifferent selectivity in term of an etching or a CMP operation. Forexample, the dielectric layer 206 b can be a silicon oxide layer,whereas the dielectric layers 206 a, 206 c can other dielectric otherthan silicon oxide. The stack of dielectric layers 206 a, 206 b, 206 ccan be formed by a variety of techniques, e.g., chemical vapordeposition (CVD), low-pressure CVD (LPCVD), plasma-enhanced CVD (PECVD),sputtering and physical vapor deposition (PVD), thermal growing, and thelike.

In FIG. 14 and FIG. 15 , two openings 1401 a, 1401 b are formedpenetrating through the stack of dielectric layers 206 a, 206 b, and 206c. As demonstrated in FIG. 14 , a first opening 1401 a is formed over acontact plug 113 electrically coupled to the doped region 105 b of thefirst region 700 a. A second opening 1401 b is formed over a contactplug 113 electrically coupled to the doped region 105 b of the secondregion 700 b. In some embodiments, a width of the first opening 1401 ais greater than a width of the second opening 1401 b. Subsequently, aconductive layer 207 is formed over the stack of dielectric layers 206a, 206 b, and 206 c as well as filling the first opening 1401 a and thesecond opening 1401 b. The conductive layer 207 may be formed by avariety of techniques, e.g., high-density ionized metal plasma (IMP)deposition, high-density inductively coupled plasma (ICP) deposition,sputtering, physical vapor deposition (PVD), chemical vapor deposition(CVD), low-pressure chemical vapor deposition (LPCVD), plasma-enhancedchemical vapor deposition (PECVD), and the like. In FIG. 15 , aplanarization operation is performed to remove the overburden of theconductive materials 207 and the dielectric layer 206 c. A lowerelectrode 202 a in the first region 700 a and a lower electrode 202 b inthe second region 700 b can be obtained at the completion of theplanarization operation. Note the lower electrode 202 a has a surfacearea different from a surface area of the lower electrode 202 b viewingfrom a top view perspective (not shown). The difference in surface areasbetween the lower electrodes 202 a and 202 b is due to the formation ofsubsequent MTJ layers having different dimensions.

In FIG. 16 , an MTJ layer 2011 having a thickness of from about 150 Å toabout 250 Å and a conductive layer 2031 are formed over the planarizedsurface shown in FIG. 15 . The MTJ layer 2011 is formed on the lowerelectrodes 202 a, 202 b and patterned dielectric stacks 206 a, 206 b.The MTJ layer 2011 may be formed by variety of techniques, e.g.,high-density ionized metal plasma (IMP) deposition, high-densityinductively coupled plasma (ICP) deposition, sputtering, physical vapordeposition (PVD), chemical vapor deposition (CVD), low-pressure chemicalvapor deposition (LPCVD), plasma-enhanced chemical vapor deposition(PECVD), and the like. In some embodiments, the MTJ layer 2011 is astack of various deposited films. Detailed structure of the MTJ layer2011 is previously described in FIG. 5 and FIG. 6 , and is not repeatedhere for simplicity. The conductive layer 2031 may be formed by avariety of techniques, e.g., high-density ionized metal plasma (IMP)deposition, high-density inductively coupled plasma (ICP) deposition,sputtering, physical vapor deposition (PVD), chemical vapor deposition(CVD), low-pressure chemical vapor deposition (LPCVD), plasma-enhancedchemical vapor deposition (PECVD), and the like.

In FIG. 17 , a mask layer 1701 is formed on the conductive layer 2031.The mask layer 1701 may have a multi-layer structure, which may include,for example, an oxide layer, an advanced patterning film (APF) layer andan oxide layer. Each of the oxide layer, the APF layer, and the oxidelayer may be formed by a variety of techniques, e.g., high-densityionized metal plasma (IMP) deposition, high-density inductively coupledplasma (ICP) deposition, sputtering, physical vapor deposition (PVD),chemical vapor deposition (CVD), low-pressure chemical vapor deposition(LPCVD), plasma-enhanced chemical vapor deposition (PECVD), and thelike. In some embodiments, the mask 1701 is configured to pattern theMTJ layers 201 a, 201 b and upper electrodes 203 a, 203 b shown in FIG.18 . For example, a width of the openings 1701 a, 1701 b of the masklayer 1701 are determined according to the desired MTJ diameter. Aspreviously discussed, the first MTJ layer 201 a in the first region 700a possesses a bottom diameter D1 of from about 10 nm to about 60 nm froma top view perspective, and the second MTJ layer 201 b in the secondregion 700 b possesses a bottom diameter D1′ smaller than that of D1. Insome embodiments, the MTJ layers 201 a, 201 b and the upper electrodes203 a, 203 b are formed to have a trapezoidal shape viewing from thecross section.

In FIG. 19 , a dielectric layer 2041 is conformally formed over the MTJlayers 201 a, 201 b and the upper electrodes 203 a, 203 b. In someembodiments, the dielectric layer 2041 possesses a thickness of fromabout 50 Å to about 300 Å. Note a sidewall of the MTJ layers 201 a, 201b and the sidewall of lower electrode 202 a, 202 b are surrounded by thedielectric layer 2041 to prevent oxidation or other contamination.Subsequently, a dielectric layer 2051 such as an oxide layer isconformally deposited over the dielectric layer 2041. In FIG. 20 , aplanarization operation is performed on the dielectric layer 2051 suchthat a top surface of the 1 o dielectric layer 2051 is substantiallyflat. This planarization operation is a preparation step for thefollowing thinning operation where starting with a substantially flatsurface is crucial to said thinning operation. As shown in FIG. 20 , atop surface of the MTJ layer 203 a, 203 b is not exposed from thedielectric layer 2041 after the planarization operation.

Referring to FIG. 21 and FIG. 22 , the vias 119 are formed over theconductive plugs 113. In some embodiments, multiple openings 119′ arepatterned through the dielectric layers 2051, 2041, 206 b, and 206 auntil the conductive plug is exposed. Subsequently, conductive materialis filled into the openings 119′, followed by a thinning operationremoving the overburden of the conductive material and a portion of thedielectric layers 2051, 2041. Noted in FIG. 22 a top surface 2031 a ofthe MTJ layer 203 a is exposed as a result of the thinning operation.

Referring to FIG. 23 , FIG. 24 , and FIG. 25 , a first metalinterconnect M₁ including vias 119 and metal lines 117 connecting vias119 are formed over the vias 119 at the same level with the MRAM cell.In FIG. 23 , an etch stop layer (ESL) 208, an IMD 115′ and a maskinglayer 209 are blanket deposited over the planarized surface in FIG. 22 .The IMD 115′, the ESL, and the masking layer 209 can be formed by avariety of techniques for forming such layers, e.g., chemical vapordeposition (CVD), low-pressure CVD (LPCVD), plasma-enhanced CVD (PECVD),sputtering and physical vapor deposition (PVD), thermal growing, and thelike. Trenches to be filled with conductive materials are patterned overthe vias 119 at the same level with the MRAM cell. In FIG. 24 ,conductive materials are filled into the trenches. After anotherplanarization operation, a dielectric layer 2061 is formed over thefilled trenches and metal lines 117 are formed using, for example,Damascene operation.

In FIG. 26 , upper metal layer such as M₃, M₄ . . . M_(top) are formedover the first metal interconnect M₁ and construct the interconnectstructure over the MRAM cell.

The integrated circuit device may undergo further CMOS or MOS technologyprocessing to form various features known in the art. For example, oneor more contact features (not shown), such as silicide regions, may alsobe formed. The contact features may be coupled to the source and drain.The contact features comprise silicide materials, such as nickelsilicide (NiSi), nickel-platinum silicide (NiPtSi),nickel-platinum-germanium silicide (NiPtGeSi), nickel-germanium silicide(NiGeSi), ytterbium silicide (YbSi), platinum silicide (PtSi), iridiumsilicide (IrSi), erbium silicide (ErSi), cobalt silicide (CoSi), othersuitable conductive materials, and/or combinations thereof. In anexample, the contact features are formed by a salicide (self-alignedsilicide) process.

Subsequent processing may further include forming variouscontacts/vias/lines and multilayer interconnect features (e.g., metallayers and interlayer dielectrics) over the substrate, configured toconnect the various features or structures of the integrated circuitdevice. The additional features may provide electrical interconnectionto the device including the formed metal gate structures. For example, amultilayer interconnection includes vertical interconnects, such asconventional vias or contacts, and horizontal interconnects, such asmetal lines. The various interconnection features may implement variousconductive materials including copper, tungsten, and/or silicide. In oneexample a damascene and/or dual damascene process is used to form acopper related multilayer interconnection structure.

The present disclosure provides a semiconductor structure including asubstrate, a transistor region having a gate over the substrate and adoped region at least partially in the substrate, a first metalinterconnect over the transistor region, and a magnetic tunnelingjunction (MTJ) between the transistor region and the first metalinterconnect. A first region over the substrate including a firstmagnetic tunneling junction (MTJ) between the transistor region and thefirst metal interconnect, and a second region over the substrate notoverlapping with the first region.

The present disclosure provides a semiconductor structure including asubstrate, a transistor region having a gate over the substrate and adoped region at least partially in the substrate, and a first metalinterconnect over the transistor region.

The present disclosure provides a method for manufacturing asemiconductor structure, including forming a transistor region over asubstrate, the transistor region comprising a gate and a doped region,forming a magnetic tunneling junction (MTJ) over the transistor region,electrically coupling to the transistor region, and forming a firstmetal interconnect over the MTJ, electrically coupling to the MTJ andthe transistor region.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations cancan be made herein without departing from the spirit andscope of the invention as defined by the appended claims. For example,many of the processes discussed above cancan be implemented in differentmethodologies and replaced by other processes, or a combination thereof.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will 1 oreadily appreciate from the disclosure of the present invention,processes, machines, manufacture, compositions of matter, means,methods, or steps, presently existing or later to be developed, thatperform substantially the same function or achieve substantially thesame result as the corresponding embodiments described herein may beutilized according to the present invention. Accordingly, the appendedclaims are intended to include within their scope such processes,machines, manufacture, compositions of matter, means, methods, or steps.

What is claimed is:
 1. A semiconductor structure, comprising: asubstrate; a transistor region, comprising a gate over the substrate,and a doped region at least partially in the substrate; a metalinterconnect over the doped region, and the metal interconnect comprisesa metal via; and a magnetic tunneling junction (MTJ) entirely underneaththe metal interconnect and between the doped region and the metal via,and a diameter of a bottom surface of the MTJ is greater than a diameterof an upper surface of the MTJ.
 2. The semiconductor structure of claim1, wherein the MTJ comprises a plurality of ferromagnetic layers and aplurality of spacers stacked alternately between the doped region andthe metal via.
 3. The semiconductor structure of claim 2, wherein thespacers comprises non-ferromagnetic metal.
 4. The semiconductorstructure of claim 1, further comprising: an upper electrode under themetal interconnect; and a lower electrode directly over the metal via;wherein a diameter of the lower electrode is greater to a diameter ofthe upper electrode.
 5. The semiconductor structure of claim 4, whereina sidewall of the upper electrode is non-coplanar with a sidewall of thelower electrode.
 6. The semiconductor structure of claim 4, wherein theMTJ comprises: a pinned layer in contact with the lower electrode; afree layer on the pinned layer; and a capping layer on the free layer,wherein each of the pinned layer and the free layer comprises at least aferromagnetic layer and at least a spacer.
 7. The semiconductorstructure of claim 6, wherein the capping layer comprisesnon-ferromagnetic material.
 8. A semiconductor memory structure,comprising: a substrate; a first transistor region, comprising a firstgate and a first doped region; a second transistor region at the sameheight level as the first transistor region, comprising a second gateand a second doped region; an interconnect layer over the firsttransistor region and the second transistor region; a first magnetictunneling junction (MTJ) directly over the first doped region and underthe interconnect layer; and a second magnetic tunneling junction (MTJ)directly over the second doped region and under the interconnect layer;wherein a diameter of a top of the first MTJ is greater than a diameterof a top of the second MTJ.
 9. The semiconductor memory structure ofclaim 8, wherein a diameter of a bottom of the first MTJ is greater thana diameter of a bottom of the second MTJ.
 10. The semiconductor memorystructure of claim 8, further comprising a first contact plug betweenthe first doped region and the first MTJ.
 11. The semiconductor memorystructure of claim 10, further comprising a second contact plug betweenthe second doped region and the second MTJ.
 12. The semiconductor memorystructure of claim 8, wherein a height of the first MTJ is differentfrom a height of the second MTJ from a cross sectional perspective. 13.The semiconductor memory structure of claim 8, wherein the interconnectlayer comprises a metal via and a metal line, the metal via is incontact with a first upper electrode directly connected to the firstMTJ.
 14. The semiconductor memory structure of claim 8, wherein thefirst MTJ comprises a free layer and a pinned layer, the pinned layer iscloser to the first doped region than the free layer.
 15. Thesemiconductor memory structure of claim 8, wherein the first MTJcomprises a free layer and a pinned layer, the free layer is closer tothe first doped region than the pinned layer.
 16. A semiconductorstructure, comprising: a substrate; a transistor region, comprising agate over the substrate, and a doped region at least partially in thesubstrate; a metal interconnect over the doped region, the metalinterconnect comprises a metal via; and a magnetic tunneling junction(MTJ) between the doped region and the metal via, and the MTJ comprisesa plurality of ferromagnetic layers and a plurality of spacers stackedalternately, and a bottom diameter of each of the ferromagnetic layersand the spacers are different.
 17. The semiconductor structure of claim16, wherein a diameter of an upper surface of the MTJ is smaller than adiameter of a bottom surface of the MTJ by 20% to 50%.
 18. Thesemiconductor structure of claim 16, wherein the MTJ further comprises acapping layer over the ferromagnetic layers and the spacers.
 19. Thesemiconductor structure of claim 16, further comprising a contact plugin contact with the doped region and a lower electrode under the MTJ.20. The semiconductor structure of claim 19, wherein a sidewall of theMTJ and a sidewall of the lower electrode are surrounded by a protectionlayer.